With progress in technologies and economy and the ever-decreasing costs in automobile manufacturing and selling prices, popularity in motor vehicles has increased drastically in recent years. This not only brings convenience to people but also shortens the distances among them, satisfying the human needs for transportation. After years of research and design efforts by the manufacturers, the material used in wheels for motor vehicles has advanced from iron to aluminum, which provides lighter weight and a more appealing appearance. The progress in automobile wheel making not only improved the performance and running distance of vehicles, it also elevated the automobile industry to a higher technical realm. To obtain a leading position, all manufacturers are directing their focus in wheel manufacturing and design toward lower costs, better quality and faster production.
A prior method of producing aluminum alloy wheels is by die-casting. A large scale machine with a built-in wheel forming die is used. Melted liquid metal is cast and filled into the die. When said liquid metal cools and hardens in said die, the die is then opened to obtain a semi-finished aluminum wheel. However, with this procedure, air is likely to be trapped in the cast aluminum, resulting in air leakage and affecting safety.
In addition to the safety issue, a main drawback in said die-casting wheel manufacturing procedure is that it requires a high processing cost. Both the die and the large scale machine are very expensive and a large scale suspension system has to be installed in the factory to incorporate said wheel forming die. To remove or replace a forming die, a hoist might even be required. Therefore the prior method not only consumes substantial amount of time and takes up huge space, but also creates safety issues in the process. Those problems become even more obvious when producing larger sized wheels.
As a result, some manufacturers developed other methods of manufacturing aluminum alloy wheels. U.S. Pat. No. 4,589,177 by Secolo et al. and U.S. Pat. No. 4,185,370 provides examples of those methods. Refer to FIGS. 1–3. A flat strip 10 of aluminum alloy is first produced and then said strip 10 is bent to form a circle so that the two ends of said strip 10 are close to each other and form a small weld line 100. The weld line 100 is then welded to form said strip 10 into a hoop 12. Said hop 12 then undergoes a sequence of deformation steps by pressing rollers with different die shapes on said hoop 12 to gradually form the desired cross-sectional profile and obtain a semi-finished aluminum alloy wheel 14.
In said conventional manufacturing process, numerous sets of rollers with various shapes of dies must be utilized to sequentially press on said flat-profiled hoop 12 so that the desired cross-sectional profile on said aluminum alloy wheel 14 can be achieved. This kind of process presents several drawbacks. First, purchase and installation of many sets of expensive rollers calls for a substantial raise in cost. Secondly, the deformation process using sets of rollers with different die shapes notably increases the complexity of the working cycle, thus brings extra overheads in operation time, manpower and energy consumption. Moreover, said rolling deformation performed on said flat-profiled hoop 12 could easily create an uneven pressure during the deformation process, causing an unbalanced weight or a low hardness on the resulting aluminum alloy wheel 14, which will significantly reduce the life time of said conventionally made aluminum alloy wheel 14.